1. Field of the Invention
This invention relates generally to machines for automatically belling the ends of plastic pipe, and particularly to such machines as are designed to bell a plurality of pipe ends simultaneously under compression.
2. Description of the Prior Art
Numerous machines have been heretofore devised for belling plastic pipe. As such machines were originally developed, provision was made first for heating the end of the plastic pipe and then moving it into axial alignment with a mandrel, at which point the pipe and/or mandrel would be moved relative to each other to insert the mandrel into the pipe end to expand the same. Thereupon, the mandrel would be left in the pipe end until the pipe end cooled. The mandrel and/or pipe end would then be oppositely moved relative to each other to effect a withdrawal of the mandrel from the pipe end, and the pipe end would then be discharged from the machine. An illustration of this method of belling pipe is found in U.S. Pat. No. 3,910,744 issued Oct. 7, 1975. Some other patents similarly illustrating this simple technique are the following:
______________________________________ U.S. Pat. No. Issued ______________________________________ 3,923,443 December 2, 1975 3,205,535 September 14, 1965 3,360,826 January 2, 1968 ______________________________________
Due to the fact that cooling of plastic pipe on the mold has required a certain minimum time, i.e., generally not less than half a minute, and this slowed the production rate of belled pipe, efforts were undertaken by belling machine builders to circumvent this minimum time requirement for cooling of plastic pipe ends. One approach was, in effect, simply to provide a plurality of pipe belling lines operating side by side, thereby to double or triple the number of pipe ends which the machine could bell in the same length of time. This technique is illustrated in U.S. Pat. No. 3,672,804, granted June 27, 1972 to Dalik.
The present inventors, however, developed another approach to increasing the rate at which a belling machine could bell pipe as illustrated in their prior U.S. Pat. No. 3,932,094, issued Jan. 13, 1976. As may be seen from this last mentioned patent, the mandrel is moved with the pipe during its cooling period, to make room for a succeeding mandrel which may be inserted in the next pipe to be belled.
By whatever technique belling has thus been accomplished, due to a number of factors, such as pipe shrinkage after removal from the mandrel, the internal configuration of the belled pipe end had not proved to be sufficiently precise to meet the standards of the Underwriters Laboratories. Consequently, the present inventors more recently invented a compression type belling machine which is disclosed and claimed in their co-pending application Ser. No. 717,874, filed Aug. 26, 1976, now U.S. Pat. No. 4,059,379 issued Nov. 22, 1977, to which reference is hereby made. In effect, this last mentioned belling machine places the softened pipe end in a mold cavity precisely defining the desired external configuration for the pipe end after belling, and provision is made for the insertion of the mandrel into the pipe end while it is held in this mold cavity. After insertion of the mandrel, a sleeve-like compressor moves along and toward the end of the mandrel until it contacts and then compresses axially the exposed pipe end in the mold. This axial compression of the pipe end causes it to conform to both the precise external configuration and dimensions of the encircling mold and also to the precise internal configuration and dimensions of the mandrel itself. Upon cooling, the thus-compressed and formed pipe end retains its precise configuration and dimensions.
Thus, while the pipe belling machine art has evolved to provide both for rapid belling of pipe ends and also the compression belling of the same, no machine has heretofore been developed to accomplish both rapid belling and compression of pipe ends, despite the need for such a machine which can produce at a rapid rate belled pipe ends which will conform to the standards of the Underwriters Laboratories.